Deflectable interconnect

ABSTRACT

A package for connecting an integrated circuit to a printed circuit board. The package includes an interconnect having a deflectable cantilever and a solder bump. When the integrated circuit is affixed to the interconnect, the solder bump deflects the cantilever. When the solder bump is heated such that the solder reflows, the cantilever springs toward its non-deflected position and is at least partially absorbed by the reflowing solder.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.09/352,802, filed Jul. 13, 1999, titled, “DEFLECTABLE INTERCONNECT.” NowU.S. Pat. No. 6,285,081.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates in general to integrated circuit packagesand more particularly to ball grid array (BGA) packages.

2. Background

An increasing consideration in the design and use of integrated circuitsis the package in which the integrated circuit (IC) resides. As ICsbecome more complex, and printed circuit boards become more crowded, ICpackages continually need more leads or pins while their footprintsconsume smaller and smaller areas. In an effort to meet these demands,developers created the ball grid array (BGA) package.

A typical BGA package includes an IC affixed to a flexible polymidetape. A very thin conductor or wire bond connects a pad on the IC to aconductive trace on the polymide tape. The conductive trace is routed toa solder ball. The solder ball is one of an array of solder balls thatconnect to the opposite side of the polymide tape and protrude from thebottom of the BGA package. These solder balls interconnect with an arrayof pads located on a substrate, such as a printed circuit board.Accordingly, the typical BGA package electrically connects each pad onan IC to a pad on a printed circuit board.

Typical BGA packages have drawbacks arising from the differentcoefficients of thermal expansion for the IC and the polymide tape. Ingeneral, the coefficient of thermal expansion of a material correspondsto the degree in which the material will expand when heated and contractwhen cooled. As the IC and the polymide tape expand and contract atdifferent rates, the wire bond experiences stress and tension. Suchstress and tension may cause the wire bond to loosen or break, therebydisconnecting the IC from the printed circuit board.

To compensate for stress and tension caused by thermal expansion,designers have developed IC packages without wire bonds. Oneconventional package is a “flip chip” package. A flip chip packageincludes an IC affixed to a polymide tape with a thick adhesive suchthat the pads of the IC are positioned over a layer of conductivetraces. Gaps in the adhesive provide room for a plurality of solderbumps that are used to connect the pads of the IC to the conductivetraces. Similar to the typical BGA package, the conductive traces arerouted to downward facing solder balls, which connect with pads of asubstrate, such as a printed circuit board.

Accordingly, the solder bumps of the flip chip package provide anelectrical connection from the pads of the IC to the layer of conductivetraces. Unfortunately, several drawbacks of these packages can prevent agood electrical connection from happening. For example, the solder bumpand adhesive dimensions need to be matched with a great deal ofaccuracy. When the solder bump diameter is small as compared to thethickness of the adhesive, the solder bump cannot connect the pads ofthe IC to the conductive traces. On the other hand, when the solder bumpdiameter is large as compared to the thickness of the adhesive, then theadhesive layer cannot sufficiently affix the IC to the tape.Furthermore, when the solder bumps are heated to cause the solder toreflow, air pockets or bubbles can form. These air pockets not only makefor a poor electrical connection, but also further exacerbate therelatively narrow tolerances allowed for the solder bump and adhesive.

These drawbacks can cause the loss of an electrical connection betweenthe IC pads and the conductive traces. Such loss lowers yield rates,which in turn increases the overall cost of package manufacture.

SUMMARY OF THE INVENTION

One aspect of the invention is to provide a package having an electricalconnection between an IC and an interposer. The package comprises asolder bump, a solder ball, and an interconnect having a deflectablecantilever. When the IC is affixed to the interconnect, the solder bumpapplies surface tension to the deflectable cantilever, thereby causingthe cantilever to deflect downward. When the solder bump is heated andthe solder reflows, the reflowing solder releases the surface tension onthe cantilever. According to one aspect of the invention, the cantileverthen springs back toward its original position, within the reflowingsolder. Thus, the reflowing solder partially absorbs the cantilever.

In one embodiment, use of a deflectable cantilever advantageouslyprovides for greater absorption of the interconnect into the solder,thereby reducing the possible effects of air pockets. In anotherembodiment, use of a larger diameter solder bump advantageously providesmore solder, thereby also reducing the possible effects of air pockets.

Another aspect of the invention relates to a ball grid array package foran integrated circuit. The ball grid array package interconnects aplurality of solder bumps-on an integrated circuit with a plurality ofsolder balls located on the exterior of the ball grid array package. Theball grid array package comprises at least one solder bump attached toan integrated circuit and at least one solder ball which is configuredto interface with a printed circuit board. The ball grid array packagefurther comprises an interposer with at least one pocket and at leastone via, wherein the pocket is configured to receive the solder bump andwherein the via is configured to receive the solder ball.

The ball grid array package further comprises a conductive interconnectcircuit which electrically interconnects the solder ball in the via withthe solder bump in the pocket. The conductive interconnect circuitfurther comprises at least one deflectable cantilever which extends intothe pocket such that the deflectable cantilever is partially absorbed bythe solder bump the pocket.

One embodiment of the invention relates to an integrated circuit packagethat comprises at least one solder connection attached to an integratedcircuit. The integrated circuit package further comprises a substratewith an opening which is configured to receive the solder connectionattached to the integrated circuit. The integrated circuit package alsocomprises a resilient cantilever which extends into the opening suchthat the resilient cantilever applies pressure to the solder connectionduring reflow.

Another embodiment of the invention relates to an apparatus thatcomprises an interconnect layer with a first opening. The apparatusfurther comprises a conductor layered above the interconnect layer. Theconductor comprising a deformable portion that extends into the firstopening, wherein the deformable portion has resiliency that urges thedeformable portion into a solder connection.

An additional embodiment relates to an integrated circuit package thatcomprises a first solder connection in communication with an integratedcircuit. The integrated circuit package further comprises aninterconnect layer having a first opening. The integrated circuitpackage also comprises a conductor layered above the interconnect layer.The conductor comprising a deflectable portion that extends into thefirst opening, wherein the deflectable portion has resiliency that urgesthe deflectable portion into the solder connection during reflow.

One embodiment of the invention relates to an apparatus comprising asubstrate with an opening. The apparatus further comprising a conductivelayer above the interconnect layer. The conductive layer comprising atleast two malleable portions which extend into the opening. In anotherembodiment a package comprises an integrated circuit having a pad and asolder connection in communication with the pad. The package furthercomprises a partially deflected first conductor and a partiallydeflected second conductor. The partially deflected first and secondconductors each at least partially absorbed by the solder connection.

In an additional embodiment, an apparatus comprises a substrate with anopening. The apparatus further comprises a conductive layer above theinterconnect layer. The conductive layer comprising at least two flapswhich extend into the opening. Yet another embodiment relates to apackage that comprises an integrated circuit having a pad and a solderbump in communication with the pad. The package further comprises adeflectable conductor having partially deflected multiple flaps. Thepartially deflected multiple flaps are at least partially absorbed bythe solder bump, wherein the absorption of the partially deflectedmultiple flaps is caused by the partially deflected multiple flapsmoving from a deflected position toward a non-deflected position whenthe solder bump reflows.

One embodiment of the invention relates to a package for an integratedcircuit that comprises an adhesive having a thickness and a solder bumphaving a diameter greater than the adhesive thickness. The packagefurther comprises a conductive trace having a deflectable cantilever,wherein the deflectable cantilever deflects into a pocket when theadhesive layer affixes the integrated circuit to the conductive trace.The cantilever also springs toward its original position when the solderbump reflows. The package also comprises a solder ball and a tapeattached between the conductive trace and the solder ball.

Another embodiment of the invention relates to a method for forming apackage for an integrated circuit that comprises attaching a solder bumpto an integrated circuit and forming a pocket in an interposer. Themethod further comprises tracing an interconnect over the interposersuch that a deflectable portion of the interconnect extends over aportion of the pocket. The method also comprises affixing the integratedcircuit to the interposer such that the solder bump deflects thedeflectable portion of the interconnect into the pocket.

An additional embodiment relates to a method for forming a package foran integrated circuit. The method comprises heating a solder bump to atleast partially melt the solder bump. The method further comprisesallowing a deflectable portion of an interconnect to spring toward anon-deflected position of the deflectable portion. The method alsocomprises partially absorbing the deflectable portion into the solder ofthe solder bump.

Yet another embodiment of the invention relates to a method for forminga package for an integrated circuit. The method comprises forming aninterconnect with at least two resilient conductors. The method furthercomprises deflecting the two resilient conductors with solder andheating the solder to at least partially melt the solder. The methodalso comprises allowing the two resilient conductors to spring into atleast a portion of the solder.

One embodiment of the invention relates to a method for forming apackage for an integrated circuit. The method comprises forming aninterconnect with at least one deflectable flap and deflecting the flapwith solder. The method further comprises heating the solder to at leastpartially melt the solder and allowing the flap to be absorbed by atleast a portion of the solder bump.

Another embodiment of the invention relates to a method for forming anelectrical connection between solder and a conductive material. Themethod comprises using solder to apply a surface tension on adeflectable portion of a conductive material, thereby deflecting thedeflectable portion. The method further comprises heating the solderbeyond a melting point, thereby substantially reducing the surfacetension on the deflectable portion. The method also comprises partiallyabsorbing the deflectable portion into the solder as the deflectableportion springs back toward its approximate original position.

An additional embodiment of the invention relates to a method forforming an electrical connection between solder and a conductivematerial. The method comprises using solder to deflect a cantilever andheating the solder beyond a melting point. The method further comprisespartially absorbing the cantilever into the solder as the cantileversprings back toward a non-deflected position.

Yet another embodiment of the invention relates to a method for formingan electrical connection between solder and a conductive material. Themethod comprises using solder to deflect a cantilever from a firstposition to a second position and heating the solder beyond a meltingpoint. The method further comprises at least partially absorbing thecantilever into the solder such that the cantilever moves from a secondposition to a third position.

One embodiment of the invention relates to a device that comprises meansfor affixing an integrated circuit to a conductive layer. The devicefurther comprises means for deflecting the conductive layer and thenpartially absorbing the conductive layer, thereby electricallyconnecting the integrated circuit to the conductive layer.

For purposes of summarizing the invention, certain aspects, advantagesand novel features of the invention have been described herein above. Ofcourse, it is to be understood that not necessarily all such advantagesmay be achieved in accordance with any particular embodiment of theinvention. Thus, the invention may be embodied or carried out in amanner that achieves or optimizes one advantage or group of advantagesas taught herein without necessarily achieving other advantages as maybe taught or suggested herein. Furthermore, Other aspects and advantagesof the invention will be apparent from the detailed description, theaccompanying drawings and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is described in more detail below in connectionwith the attached drawings, which are meant to illustrate and not tolimit the invention, and in which:

FIG. 1A is an exploded view of an electrical device, in accordance withone embodiment of the invention;

FIG. 1B is a cross-sectional view of the electrical device of FIG. 1A;

FIG. 2 is a cross-sectional view of a package having a deflectablecantilever, prior to attachment of an IC, according to anotherembodiment;

FIG. 3 is a top view of the deflectable cantilever of FIG. 2;

FIG. 4 is a cross-sectional view of the package of FIG. 2, afterattachment of the IC;

FIG. 5 is a cross-sectional view of the package of FIG. 2, after reflowof the solder bump;

FIG. 6 is a cross-sectional view of a package having dual deflectablecantilevers, prior to attachment of an IC, according to yet anotherembodiment;

FIG. 7 is a top view of the dual deflectable cantilevers of FIG. 6;

FIG. 8 is a cross-sectional view of the package of FIG. 6, afterattachment of the IC;

FIG. 9 is a cross-sectional view of the package of FIG. 6, after reflowof the solder bump; and

FIG. 10 is a top view of a multi-flap cantilever, according to yetanother embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

While illustrated in the context of forming an electrical connectionbetween an IC and an interposer, the skilled artisan will findapplication for the deflectable cantilever disclosed herein a widevariety of contexts. For example, the disclosed deflectable cantileverhas utility in providing an electrical connection when solder is used asa conductor, such as within a BGA package.

FIGS. 1A and 1B illustrate an electrical device 100, including a package105, and a substrate 110. FIG. 1A illustrates an exploded view of theelectrical device 100, while FIG. 1B illustrates a cross sectional viewof the same. The electrical device 100 finds use in a variety ofapplications. For example, the package 105 can be used in any electroniccircuit needing the attachment of an integrated circuit or the die 115to the substrate 110, such as the attachment of a microprocessor to aprinted circuit board.

In the illustrated embodiment of FIGS. 1A and 1B the package 105comprises the die 115, pads 120, solder bumps 125, an adhesive 130, aninterposer 135 having interconnects 140, and solder balls 145. The die115 will be understood by one of ordinary skill in the art to be anyintegrated circuit. For example, the die 115 can be from a wide range ofintegrated circuit products, such as: microprocessors, co-processors,digital signal processors, graphics processors, microcontrollers, memorydevices, reprogrammable devices, programmable logic devices, and logicarrays. In one embodiment, the die 115 comprises a memory device.

The pads 120 are shown in broken lines to indicate that they are on thereverse side of the die 115. In one embodiment, the pads 120electrically connect the die 115 to a variety of other devices, signals,or other “off chip” systems. It will be understood by one of skill inthe art of semiconductor package design that throughout the disclosure,the number of pads 120, solder bumps 125, interposer 135, interconnects140, solder balls 145, etc. are illustrated for clarity with only a fewexamples. In reality, there may be many pads 120 on the die 115. Forexample, commercially available memory devices from Micron Technology,Inc. include a 60-pin DRAM and a 100-pin SRAM, having 60 and 100 pads,respectively.

The pads 120 are electrically connected to the solder bumps 125. Suchconnection can be by commercially available processes, such as thoseoffered by Flip Chip Tech. In one embodiment, the solder bumps 125 aresmall approximate spheres of solder. However, it will be understood thata wide variety of shapes could be used. For example, the solder bumps125 could be in the shape of a pin or a cylinder or be any type ofsolder connection.

As illustrated in FIG. 1B, the package 105 includes the adhesive 130 foraffixing the die 115 to the interposer 135 and the interconnects 140. Inone embodiment, the adhesive 130 includes a number of adhesive gaps oradhesive pockets 133, which make room for the solder bumps 125. Theadhesive 130 should also be strong enough to properly affix the die 115to the interposer 135 and the interconnects 140, such that the solderbumps 125 deflect a portion of the interconnects 140, as discussed inmore detail below. In one embodiment, the adhesive 130 comprises athermal plastic polymer, however, it will be understood that theadhesive 130 can be a variety of products. For example, the adhesive 130can comprise any thermal set, thermal plastic, or any adhesive. Suchproducts are commercially available from various manufactures such as:Ablestik, Sumioxy, Dow Corning, and Hitachi.

As illustrated in FIG. 1A, the interconnects 140 are conductive paths ortraces from the physical locations of the solder bumps 125 to thephysical locations of the solder balls 145. In one embodiment, theinterconnects 140 are a resilient, yet malleable conductive materialsuch that they provide spring or memory as well as conductivity. Forexample, when a surface tension is placed on the interconnects 140, theyshould deflect in a direction corresponding to the surface tension. Whenthe surface tension is removed, the interconnects 140 “spring” back inthe direction of their original position. A wide variety of conductivematerials exhibit such properties. For example, in one embodiment, theinterconnects 140 include gold plated copper. However, it is understoodthat other conductive materials and combinations are also suitable, suchas, but not limited to, copper, gold, aluminum, and various alloys.

The interconnects 140 can also comprise a wide variety of tracepatterns, in a wide variety of sizes and layers. For example, theinterconnects 140 trace from the physical positions of the solder bumps125 to the physical positions of the solder balls 145 along a singlelayer. However, it is understood that multiple layers of theinterconnects 140 could trace through multiple layers of the interposer135 in order to provide sufficient physical space for the amount of theinterconnects 140 needed to correspond to the amount of pads 120 on thedie 115.

In one embodiment, the interposer 135 provides on one side a surfaceupon which the interconnects 140 are traced, and on the other side aconnecting point for the solder balls 145. In one embodiment, theinterposer 135 is a flexible “tape” substrate comprising insulatingmaterial, such as polymide tape. It is understood that other substratescould also be used, such as thermoplastic, thermoplast, epoxy, flexcircuits, printed circuit board materials, or fiber materials. Polymidetape and analogous materials are commercially available from Shinko,Sumitomo, Compass, 3M, Casio, Packard-Hughes, Hitachi Cable, Cicorel,Shindo, Mitsui MS, and Rite Flex.

Further, the interposer 135 includes the vias 150 for attaching thesolder balls 145 to the interconnects 140. In one embodiment, the vias150 correspond to a pre-defined pattern of the solder balls 145 for thepackage 105. Using pre-defined patterns for the solder balls 145 allowsthe output mechanisms, e.g., the solder balls 145, to remain constantover changing patterns of the pads 120 corresponding to changing the die115. In such packages, the interposer 135 is customized on the sidefacing the interconnects 140. For example, the interposer 135 would becustomized by the tracing of the interconnects 140 from the pre-definedpattern of the vias 150 to corresponding physical locations of the pads120 on the die 115.

However, it will be understood that the pattern of the solder balls 145need not be pre-defined. Rather, the interposer 135 could have apre-defined pattern for the physical location of the pads 120, and usethe interconnects 140 to trace to the vias 150 connected to a customizedpattern of the solder balls 145. Alternatively, the interconnects 140could connect customized patterns for both the pads 120 and the solderballs 145.

Furthermore, in one embodiment, the interposer 135 includes deflectionpockets 155. The deflection pockets 155 exist on the interconnect-facingside of the interposer 135. Deflectable portions, or cantilevers 160, ofthe interconnects 140, extend above the deflection pockets 155 such thatwhen surface tension is applied to the tops of the cantilevers 160, itcauses the cantilevers 160 to deflect downward into the deflectionpockets 155.

In one embodiment, the package 105 is mounted on the substrate 110,where the substrate 110 comprises a printed circuit board. However, itwill be understood that the substrate 110 could comprise a wide varietyof materials for a wide variety of applications. For example, in oneembodiment, the substrate 110 is a printed circuit board. One of skillin the art, however, will recognize that the substrate can include awide variety of materials including, but not limited to BT and FR4.

The substrate 110 includes conductive traces 165 electrically connectedto substrate pads 170. The substrate pads 170 are configured tocorrespond to, or match with, the physical location of the solder balls145. The conductive traces 165 trace an electrical connection from thesubstrate pads 170 to any number of “off chip” systems or signals.

FIGS. 2-5 illustrate a package 200, according to another embodiment ofthe invention. In particular, FIGS. 2 and 4 illustrate a process ofcombining elements of the package 200 in order to deflect the cantilever160 into a deflection pocket 155, while FIG. 3 illustrates a top view ofthe cantilever 160. FIG. 5 illustrates the package 200 after reflow ofthe solder in the solder bump 125. It will be understood that forclarity, FIGS. 2-5 illustrate only one electrical connection made fromthe die 115, through the solder bump 125 and interconnect 140, to thesolder ball 145. As mentioned above, the die 115 may have manyelectrical connections through many solder bumps 125 and interconnects140, to many solder balls 145.

FIG. 2 illustrates a cross-sectional view of the package 200 beforeattachment of the die 115. As shown in FIG. 2, the solder bump 125 isattached to the die 115. In addition, the interposer 135, theinterconnect 160 and the adhesive 130 are configured to receive thesolder bump 125 and the die 115. As discussed above, the interposer 135comprises the via 150 and the deflection pocket 155. In FIG. 2, thesolder ball 145 has not yet been attached to the via 150. However, itwill be understood that the solder ball 145 could be attached andtherefore, the solder ball 145 is shown in broken lines in FIGS. 2, 4-6,and 8-9.

In one embodiment, the interconnect 140 is constructed by depositinggold plated copper on to the interposer 135. Conventional etchingtechniques are then used to create a desired pattern for theinterconnect 140. In certain embodiments, the interconnect 140 is tracedon the die-facing side of the interconnect 140. As discussed in furtherdetail below, the interconnect 140 can include a cantilever 160. Theskilled artisan will recognize that the interconnect 140 can be a widerange of conductors, conductive traces or the like. Furthermore, thecantilever 160 can in certain embodiments include deflectable portions,resilient portions, deformable portions, or malleable portions of theinterconnect 140.

The adhesive 130 attaches the interposer 135 and the interconnect 140 tothe die 115. In one embodiment, the adhesive 130 is selected such thatit can withstand a temperature of at least about 150° C., for example,Sumioxy LOC Tape, manufactured by Occidental Chemical Corporation.

The adhesive layer 130 comprises at least one adhesive pocket 133. Inone embodiment, the adhesive pocket 133 extends through the adhesivelayer 130 and partially into the interposer 135. In other embodiments,the adhesive pockets 133 are holes that extend through the adhesivelayer 130 and the interposer 135. The adhesive pocket 133 is dimensionedto receive the solder bump 125. In one embodiment, the adhesive pocket133 is constructed by selectively applying adhesive to the interconnect140 and the interposer 135 using known techniques. In other embodiments,the adhesive pocket 133 is constructed by screen printing, drilling orpunching the adhesive layer 130 or interposer 135.

FIG. 3 illustrates a top view of the interposer 135 and the interconnect140. In FIG. 3, the interposer 135 includes the deflection pocket 155surrounded by the interconnect 140. In one embodiment, the deflectionpocket 155 is approximately square in shape and does not extend entirelythrough the interposer 135. However, it will be understood that a widevariety of shapes could be used to form the deflection pocket 155, forexample, approximately circular, oval, or polygonal shapes could beused. Furthermore, it will be understood that a wide variety of shapesof the interconnect 140 could be used to surround the deflection pocket155. For example, the shapes of the interconnect 140 could eithercorrespond to, or be different from, the wide variety of shapes of thedeflection pocket 155. For example, the deflection pocket 155 could bepolygonal in shape and be surrounded by the interconnect 140 in acircular fashion.

Also, the deflection pocket 155 could extend entirely through theinterposer 135 thereby creating another hole or via in the interposer135. While such a punched-through deflection pocket 155 is typicallyeasier to manufacture, it can expose the interior of the package 200 toenvironmental conditions after the die 115 and the solder ball 125 areattached.

FIG. 3 also illustrates the cantilever 160 extending over the deflectionpocket 155. In one embodiment, the cantilever 160 extends approximatelyhalf the distance across the deflection pocket 155. However, it isunderstood that one skilled in the art could manipulate the flexibilityand spring constant of the cantilever 160 by adjusting the width andlength thereof. The pattern of the interconnect 140 is shown depositedon a portion of the interposer 135 and over the defection pocket 155. Itwill be understood by one of skill in the art that the pattern of theinterconnect 140 can be adapted for a variety of patterns andsituations.

FIG. 4 illustrates a cross-sectional view of the package 200, after thedie 115 and the solder bump 125 are affixed to the adhesive 130. In oneembodiment, the diameter of the solder bump 125 is larger than thethickness of the adhesive 130, and therefore, the solder bump 125applies a surface tension to the cantilever 160. The surface tensiondeflects the cantilever 160 downward into the deflection pocket 155. Inone embodiment, the resilient deflected cantilever 160 applies apressure on the solder bump 125 that is directed towards the surface ofthe solder bump 125.

FIG. 5 illustrates a cross-sectional view of the package 200 afterreflow of the solder in the solder bump 125. When the solder in thesolder bump 125 reflows, it applies less surface tension to thecantilever 160, allowing the cantilever 160 to spring back in thedirection of the original position of the cantilever 160. As thecantilever 160 returns, it is at least partially absorbed by thereflowing solder. Thus, in one embodiment, the cantilever 160 applies aninwardly directed pressure to the solder bump 125 the urges thecantilever 160 into the solder bump 125.

It will be understood that the die 115, the solder bump 125, theadhesive 130, the interposer 135, the interconnect 140, and the solderball 145, could have a variety of sizes and thicknesses. As mentioned,the die 115 can be from a wide range of integrated circuit products. Forthis reason, the type of integrated circuit product will dictate thethickness of the die 115. In one embodiment, the die 115 is a dynamicmemory device with a thickness of approximately 280 microns. Also, inone embodiment, the thickness of the interconnect 140 and the cantilever160 is approximately 15 microns, the thickness of the interposer 135 isapproximately 48 microns, and the diameter of the solder ball 145 isapproximately 400 microns.

One advantage of the cantilever 160 is that the diameter of the solderbump 125 and the thickness of the adhesive 130 can vary over widerranges. For example, when the diameter of the solder bump 125 is largerthan the thickness of the adhesive 130, the cantilever 160 is deflectedinto the deflection pocket 155. Thus, in order to create an electricalconnection, the diameter of the solder bump 125 in the package 200 canbe as thick or thicker than the adhesive 130. In one embodiment, thediameter of the solder bump 125 is approximately 200 microns and thethickness of the adhesive 130 is approximately 176 microns.

The embodiment of FIGS. 2-5 thus provides the package 200 that haselectrical connections from the pads 120 on the die 115, through thesolder bumps 125 and the interconnects 140, to the solder balls 145. Thesolder bumps 125 deflect the cantilevers 160 when the die 115 is affixedto the adhesive 130. During reflow, the cantilevers 160 spring backtoward their original position and are thereby partially absorbed by thesolder bump 125. Deflection allows for relaxed tolerance requirementsbetween the diameter of the solder bump 125 and the thickness of theadhesive 130. Partial absorption allows for formation of an electricalconnection. These characteristics improve yield rates and therebydecrease the cost of package manufacture.

FIGS. 6-9 illustrate a package 600 according to yet another embodimentof the invention. In particular, FIGS. 6 and 8 illustrate a process ofcombining elements of the package 600 in order to deflect dualcantilevers 605 and 610 into a deflection pocket 615, while FIG. 7illustrates a top view of the dual cantilevers 605 and 610. FIG. 9illustrates the package 600 after reflow of the solder in the solderbump 125. It will be understood that for clarity, FIGS. 6-9 illustrateonly one electrical connection made from the die 115, through the solderbump 125 and interconnect 140, to the solder ball 145. As mentionedabove, the die 115 may have many electrical connections through manysolder bumps 125 and interconnects 140, to many solder balls 145.

Accordingly, FIG. 6 illustrates a cross-sectional view of the package600 before attachment of the die 115. As shown in FIG. 6, the solderbump 125 is attached to the die 115. Furthermore, the interposer 135includes the interconnect 140 traced on at least the die-facing side ofthe interposer 135. In one embodiment, the interconnect 140 is depositedon the interposer 135. Typical etching techniques are used to create adesired pattern for the interconnect 140.

The interposer 135 also includes the via 150 and the deflection pocket615. In one embodiment, the solder ball 145 has not yet been attached tothe via 150. The adhesive 130 is then added in order to cover both theinterposer 135 and the interconnect 140. The adhesive pockets 133 areadded, punched, drilled and screen printed. In certain embodiments, thepocket 615 and the via 150 comprise openings formed in the interposer135.

FIG. 7 illustrates a top view of the interposer 135 and the interconnect140. The interposer 135 includes the deflection pocket 615 surrounded bythe interconnect 140. In one embodiment, the deflection pocket 615 isapproximately square in shape and does not extend entirely through theinterposer 135. However, it will be understood that a wide variety ofshapes could be used to form the deflection pocket 615. Furthermore, itwill be understood that a wide variety of shapes of the interconnect 140could be used to surround the deflection pocket 615. For example, thedeflection pocket 615 could be polygonal in shape and be surrounded bythe interconnect 140 in a circular fashion.

FIG. 7 also illustrates the deflection pocket 615 as an alternative tothe deflection pocket 155 of FIGS. 2-5. The deflection pocket 615extends through the interposer 135. It will be understood that a skilledartisan would recognize that the deflection pocket 615 could be usedwith the embodiment of FIGS. 2-5, and likewise, the deflection pocket155 could be adapted for use in FIG. 6.

FIG. 7 also illustrates the dual cantilevers 605 and 610 extending overthe deflection pocket 615 from opposite sides. Each of the dualcantilevers 605 and 610 is similar in composition and materialconsiderations as those mentioned in reference to the cantilever 160. Inone embodiment, each of the dual cantilevers 605 and 610 has a lengthwhich is approximately half the diameter or width of the deflectionpocket 615. In other embodiments, the first cantilever 605 may beapproximately a third of the width of the deflection pocket 615 whilethe second cantilever 610 may be approximately two-thirds the width ofthe deflection pocket 615. In yet other embodiments, the dualcantilevers 605 and 610 may each be less than approximately half thewidth of the deflection pocket 615.

It will be understood that a skilled artisan would recognize a widerange of lengths and designs for the dual cantilevers 605 and 610. Forexample, directly opposite cantilevers may have a lower bound on theirlengths being dictated only by the desire for some deflection therein.Moreover, the dual cantilevers 605 and 610 may be of different lengthsin order to exhibit different deflection distances. Thereby, the dualcantilever 605 and 610 would be absorbed into different areas of thesolder bump 125.

Also, the dual cantilevers 605 and 610 could have lengths longer thanhalf the diameter, or half the width, of the deflection pocket 615 bybeing offset from direct opposition of each other. In addition to theembodiments mentioned above, it is understood that a skilled artisan mayuse other designs for the dual cantilevers 605 and 610 directed to needsrecognizable to such an artisan. Also, it is understood that one skilledin the art could manipulate the flexibility and spring constant of eachof the dual cantilevers 605 and 610 by adjusting the widths and lengthsthereof.

FIG. 8 illustrates a cross-sectional view of the package 600, after thedie 115 and the solder bump 125 are affixed to the adhesive 130. In oneembodiment, the diameter of the solder bump 125 is larger than thethickness of the adhesive 130, and therefore, the solder bump 125applies a surface tension to the dual cantilevers 605 and 610. Thesurface tension deflects the dual cantilevers 605 and 610 downward intothe deflection pocket 615.

FIG. 9 illustrates a cross-sectional view of the package 600 afterreflow of the solder in the solder bump 125. When the solder in thesolder bump 125 reflows, it applies less surface tension to the dualcantilevers 605 and 610, allowing each of the dual cantilevers 605 and610 to spring back in the direction of their original position. As thedual cantilevers 605 and 610 return, they are at least partiallyabsorbed by the reflowing solder. Partial absorption creates anelectrical connection in spite of possible air pockets or bubbles.

Similar to FIGS. 2-5, use of the dual cantilevers 605 and 610 in thepackage 600 allows the diameter of the solder bump 125 and the thicknessof the adhesive 130 to have a more relaxed relationship. For example,when the diameter of the solder bump 125 is larger than the thickness ofthe adhesive 130, the dual cantilevers 605 and 610 are deflected intothe deflection pocket 615. Thus, in order to create an electricalconnection, the diameter of the solder bump 125 in the package 600 needonly be as thick as the adhesive 130. On the other hand, the diameter ofthe solder bump 125 may be as large as the maximum deflection of thedual cantilevers 605 and 605. In one embodiment, the diameter of thesolder bump 125 is approximately 200 microns and the thickness of theadhesive 130 is approximately 176 microns.

The embodiments of FIGS. 6-9 thus provides the package 600 that haselectrical connections from the pads 120 on the die 115, through thesolder bumps 125 and the interconnects 140, to the solder balls 145. Thesolder bumps 125 deflect the dual cantilevers 605 and 610 when the die115 is affixed to the adhesive 130. During reflow, the dual cantilevers605 and 610 spring back toward their approximate original position andare thereby partially absorbed by the solder bumps 125. Deflectionallows for relaxed tolerance requirements between the diameter of thesolder bumps 125 and the thickness of the adhesive 130. Partialabsorption allows for formation of an electrical connection. Thesecharacteristics improve yield rates and thereby decrease the cost ofpackage manufacture.

FIG. 10 illustrates a top view of yet another embodiment of theinvention. Similar to FIGS. 3 and 7, FIG. 10 includes the interposer 135having a deflection pocket 1010 (shown in broken lines) surrounded bythe interconnect 140. As with the deflection pocket 155, it will beunderstood that the deflection pocket 1010 could be many shapes and theinterconnect 140 may or may not correspond to such shapes. Furthermore,the deflection pocket 1010 could extend entirely through the interposer135. However, in one embodiment, the deflection pocket 1010 isapproximately square and extends only partially through the interposer135.

As further illustrated by FIG. 10, the interconnect 140 includes aseries of flaps 1005 extending over and partially covering thedeflection pocket 1010. The flaps 1005 are made by depositing theinterconnect 140 over the deflection pocket 1010 and then etchingopenings 1015 therein. The deposition and etching are done by typicalmethods known to one of ordinary skill in the art of package design. Theopenings 1015 define the shape of the flaps 1005 and provide the abilityof the flaps 1005 to deflect downward into the deflection pocket 1010.It will be understood that the flaps 1005 could be a wide variety ofshapes and sizes. However, in one embodiment, the flaps 1005 comprisefour triangular-shaped flaps 1005, with each of the flaps 1005 havingone vertice in the approximate center of the deflection pocket 1010.

Although the foregoing invention has been described in terms of certainpreferred embodiments, other embodiments will be apparent to those ofordinary skill in the art. For example, a wide variety of shapes andsizes of both the pockets and corresponding deflectable interconnectportions may be combined to provide electrical connections within apackage. Additionally, other combinations, omissions, substitutions andmodifications will be apparent to the skilled artisan, in view of thedisclosure herein. Accordingly, the present invention is not intended tobe limited by the recitation of the preferred embodiments, but isinstead to be defined by reference to the appended claims.

What is claimed is:
 1. An integrated circuit package comprising: atleast one first solder connection attached to an integrated circuit; atleast one second solder connection; a substrate with a first openingwhich is configured to receive the first solder connection and a secondopening which is configured to receive the second solder connection; anda resilient cantilever electrically connected to a conductive trace,wherein the resilient cantilever extends into the first opening suchthat the resilient cantilever applies pressure to the first solderconnection during reflow, and wherein the conductive trace is alsoelectrically connected to the second solder connection.
 2. Theintegrated circuit package of claim 1 wherein the first solderconnection is a solder bump.
 3. The integrated circuit package of claim1 wherein the substrate comprises flexible tape.
 4. The integratedcircuit package of claim 1 wherein the substrate comprises polymide. 5.The integrated circuit package of claim 1 wherein the pressure appliedby the resilient cantilever is directed into the first solderconnection.
 6. The integrated circuit package of claim 1 wherein theresilient cantilever is partially absorbed by the first solderconnection.
 7. The integrated circuit package of claim 1, wherein thesecond solder connection comprises a solder ball.
 8. The integratedcircuit package of claim 7, wherein the solder ball is configured toelectrically connect the conductive trace to a second substrate.
 9. Anapparatus comprising: an interposer layer comprising: a first sideincluding a first set of openings; and a second side including a secondset of openings; and a plurality of interconnects, each interconnectcomprising: a deformable portion that extends into one of the first setof openings, wherein the deformable portion has resiliency that urgesthe deformable portion into a solder connection, and a solder ballconnection portion which is configured to attach to a solder ball atleast partially received into one of the second set of openings on thesecond side.
 10. The apparatus of claim 9 wherein the resiliency urgesthe deformable portion into the solder connection during reflow.
 11. Theapparatus of claim 9 wherein each of the first set of openings comprisesa pocket formed in the first side of the interposer layer.
 12. Theapparatus of claim 9 wherein the deformable portion comprises at leastone cantilever.
 13. The apparatus of claim 9, wherein the first set ofopenings comprises an array of openings.
 14. The apparatus of claim 9,wherein the second set of openings comprises an array of openings. 15.The apparatus of claim 9, further comprising an integrated circuithaving pads connected to one or more solder bumps.
 16. A packagecomprising: an integrated circuit having a pad; a solder bump incommunication with the pad; a partially deflected first conductor and apartially deflected second conductor, the partially deflected first andsecond conductors each at least partially absorbed by the solder bump; asolder ball; and a conductive trace electrically connected to the firstconductor, the second conductor, and the solder ball.
 17. The packageaccording to claim 16 wherein the first and second conductors deflect inthe same direction from opposite sides of the solder bump.
 18. Thepackage according to claim 16 wherein the first and second conductorsare each a length approximately equal to half of a diameter of thesolder bump.
 19. The package according to claim 16 wherein the first andsecond conductors comprise flaps.
 20. The package according to claim 19wherein the flaps are arranged such that an area underneath the solderbump is substantially covered when the flaps are in a non-deflectedposition.
 21. The package according to claim 16, further comprising aninsulating layer having openings, wherein the solder ball is at leastpartially recessed in one of the openings when the solder ball isconnected to the conductive trace.